An internal gear pump formed by accommodating a pump rotor, which is constituted of a combination of an inner rotor and an outer rotor that are eccentrically disposed, within a rotor chamber of a housing is used as, for example, an oil pump for lubricating a vehicle engine or for an automatic transmission (AT).
The internal gear pump has an intake port and a discharge port in an end surface of the rotor chamber of the housing. A section between a terminal end of the intake port and a start end of the discharge port serves as a containment section that separates a chamber (i.e., a pump chamber) formed between the teeth of the inner rotor and the outer rotor from the intake port and the discharge port. While the aforementioned chamber moves and increases in area (volume) toward the intake port, liquid is taken into the chamber. Moreover, while the chamber moves and decreases in area toward the discharge port, the liquid within the chamber is delivered to the discharge port.
With regard to this internal gear pump, the tooth profile of the inner rotor is formed based on the following method disclosed in Patent Literature 1. With regard to the tooth profile designed based on this method (which will be described in detail later), the tooth height can be freely increased. Therefore, by increasing the volume of the chamber, the discharge rate of the pump can be increased.
By combining the inner rotor whose tooth profile is formed based on the method disclosed in Patent Literature 1 with an outer rotor whose tooth profile is formed based on the following method disclosed in Patent Literature 2, a pump rotor with relatively smooth rotation can be realized. Therefore, the tooth profile of the outer rotor to be combined is formed based on the method disclosed in Patent Literature 2.
The method disclosed in Patent Literature 2 involves revolving the center of the inner rotor along a circle having a diameter of (2e+t) (where e denotes an amount of eccentricity between the inner rotor and the outer rotor and t denotes a tip clearance between the inner rotor and the outer rotor), and rotating the inner rotor (1/n) times per revolution. An obtained envelope of a group of tooth-surface curves of the inner rotor serves as the tooth profile of the outer rotor.